The present invention relates to an apparatus for processing a target and/or manufacturing a thin film through irradiation of the target with an ion beam. More particularly, the invention concerns an ion beam apparatus suited advantageously for manufacturing and/or processing large scale thin films and semiconductors.
As an apparatus for processing a surface of a target and/or forming a thin film on a substrate located in opposition to the target by physically sputtering or chemically etching the target through irradiation with an ion beam having energy on the order of 200 to 5000 eV, there has heretofore been known a structure schematically shown in FIG. 1 of the accompanying drawings. More specifically, referring to FIG. 1, a neutral gas or an active gas is introduced into a cylindrical plasma producing vessel 1 through a gas inlet port 2, wherein arc discharge is caused to take place between a filament 3 and an anode electrode 4 to produce plasma from which an ion beam is extracted under the influence of the electric field generated by ion extracting electrodes 5 and 6 to sputter or etch a target 7 for the processing thereof or formation of a thin film on a substrate 8 disposed in opposition to the target 7. All the components mentioned above are accommodated within a vacuum vessel 9 adapted to be evacuated by a vacuum pump 11. A solenoid coil 10 serves to enhance the efficiency at which the plasma is generated and plays an important role in allowing the apparatus to operate with a small amount of gas.
As the ion beam of an increased diameter is required to be employed in accompaniment to the tendency of thin films being formed on a larger scale, a demand arises for the use of the plasma producing vessel of a larger diameter which in turn involves the use of the solenoid coil 10 of an increased size, giving rise to a problem that leakage of the magnetic field generated by the solenoid coil 10 toward the target 7 or the substrate 8 occupies a large proportion. Obviously, such great leakage of the magnetic field makes it difficult to control the magnetic anisotropy and other properties, not to speak of degradation in performance of the apparatus. Further, the ion beam as extracted is bent under the action of the leakage field to degrade the parallelism of the ion beam, being accompanied by deterioration in the working precision.
In order to attain a high precision in the manufacture and processing of the thin film by using an ion beam, it is required that the ion beam has a high uniformity, a small angle of beam divergence and a high parallelism. In the case of the ion beam apparatus shown in FIG. 1, however, a part of plasma located in the vicinity of the inner wall of the plasma producing vessel 1 is cooled through contact with the wall of the vessel 1, bringing about loss of plasma. As the result, distribution of the plasma density becomes such that the plasma density is high at the center of the opening of the plasma producing vessel 1 and becomes low toward the end of the opening. Consequently, the plasma pressure on the surface of the extracting electrode 5 which affects the electric field formed in the apertures of the electrode becomes high at the center region of the extracting electrode and becomes low toward the periphery thereof, resulting in that the electric fields formed in the apertures of the extracting electrodes 5 and 6 become different between the apertures located at the center region and those located at the peripheral portion. Due to such nonuniformity in distribution of the plasma density and the electric field, the uniform ion beam is difficult to be produced. Accordingly, it is impossible to accomplish the high precision processing with the ion beam apparatus shown in FIG. 1.
FIG. 2 shows another ion beam apparatus known heretofore. The similar ion beam apparatus are disclosed in "Technology and Application of Broad-Beam Ion Sources used in Sputtering, Part 1, Ion Source Technology" by H. R. Kaufman et al. J. Vac. Sci. Technol., 21 (3), Sept./Oct. 1982 and "Broad-Beam Ion Sources: Present Status And Future Directions" by H. R. Kaufman, J. Vac. Sci. Technol.A4 (3), May/June 1986. The ion beam apparatus is of such a structure in which a discharge chamber is provided, which is composed of permanent magnets 100, pole pieces 101 extending inwardly of the plasma producing vessel from both ends of one permanent magnet and anode electrodes 102 each provided in a space defined by one magnet and two pole pieces, wherein the magnets 100, pole pieces 101 and the anode electrodes 102 are arrayed along the inner wall of the plasma producing vessel. The ion beam generating apparatus of this type suffers however a shortcoming that maintenance thereof is difficult. More specifically, all the corners and hidden surfaces behind the anode electrodes of the ion beam producing apparatus require cleaning, and for the cleaning, the ion beam apparatus has to be disassembled. However, great difficulty and troublesome procedure will be involved in disassembling this known ion beam producing apparatus.
Another problem of this ion beam producing apparatus is seen in that the confinement of plasma can not be achieved satisfactorily. As is shown in FIG. 2, the anode electrode is disposed at a position retracted from the tip end of the pole shoe. In other words, the anode electrode is positioned outside of the plasma confining region defined by the magnetic flux 103 formed between the tips of the pole pieces. Although electrons emitted from the filament 104 must reach the anode electrodes 102 by traversing the magnetic flux, the electrons are prevented from traversing the magnetic flux when the magnetic field is too strong. Thus, when the magnetic field is intensified with a view to confine adequately the plasma, electrons can not arrive at the anode electrode. Accordingly, the magnetic flux density is necessarily limited to less than several tens gausses which is insufficient for confining the plasma. For these reasons, the ion beam producing apparatus is incapable of accomplishing satisfactorily the plasma confinement.
Japanese Patent Application Laid-Open No. 54797/1981 (JP-A-56-54797) discloses an ion source apparatus in which permanent magnets are disposed around the plasma producing vessel. However, this ion source apparatus is not designed for use in fabrication and processing of thin films as in the case of the present invention but destined for use as a neutron injection heater apparatus for an experimental nuclear fusion equipment.
Japanese Patent Application Laid-Open No. 63799/1981 (JP-A-56-63799) discloses an ion source apparatus in which permanent magnets are disposed within a plasma generating vessel. However, this apparatus is also intended to be employed in a plasma heating neutral particle injection apparatus and can not be used for fabrication and processing of thin films as with the case of the apparatus disclosed in JP-A-56-54797 mentioned above.
Reference may be made to JP-A-61-138432 (corresponding to U.S. patent application Ser. No. 806,341 filed on Dec. 9, 1985) laid-open Jun. 25, 1986. Ion sources have been also proposed in U.S. patent application Ser. No. 911,790 filed on Sept. 26, 1986 and U.S. patent application Ser. No. 914,196 filed on Oct. 1, 1986.